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Clonidine side effects and how to avoid them

Clonidine side effects include weight changes, hair loss, and sexual dysfunction
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By | Aug. 18, 2022 Medically reviewed by Josephine Bawab, Pharm.D.

Common clonidine side effects | Serious side effects | Weight changes | Hair loss | Sexual dysfunction | Side effects timeline | Contraindications | Warnings | Interactions | How to avoid side effects  | How to treat side effects

Clonidine is a generic prescription drug taken daily as a generic tablet or weekly as a brand-name skin patch (Catapres TTS) to reduce high blood pressure (hypertension). It can also be administered as a spinal injection to help relieve severe pain due to cancer. Finally, clonidine extended-release tablets (also sold as the brand-name Kapvay) are given to children and adolescents to treat attention deficit hyperactivity disorder (ADHD). Clonidine is an alpha agonist; it affects nerves in the brain and spinal cord, reducing their effect on involuntary activities like tightening blood vessels and causing the heart to beat. As a result, blood vessels widen and the heart slows down, reducing blood pressure. This same mechanism helps shut down pain signals in the spinal cord. However, no one is certain how clonidine helps with ADHD symptoms. No matter what indication clonidine is treating, most people taking it will have one or more unwanted side effects.

Common side effects of clonidine

The most common side effects of clonidine are low blood pressure, dry mouth, and anxiety. In order of incidence, the most common side effects of clonidine are:

  • Dry mouth
  • Anxiety
  • Drowsiness
  • Dizziness
  • Itching
  • Headache
  • Infection
  • Fatigue
  • Stomach pain
  • Nausea
  • Vomiting
  • Constipation
  • Nightmares
  • Irritability
  • Insomnia
  • Loss of appetite
  • Excessive sweating
  • Darkening of the skin
  • Urinary incontinence
  • Shaking
  • Stuffy nose
  • Tiredness
  • Decrease in sexual interest
  • Sore throat
  • Mood changes

Low blood pressure is the most common side effect of clonidine spinal injections. The others include:

  • Orthostatic hypotension (a sudden drop in blood pressure when standing)
  • Slowed heart rate
  • Rebound high blood pressure
  • Dry mouth
  • Nausea
  • Confusion
  • Dizziness
  • Sleepiness
  • Fever
  • Nausea and vomiting
  • Chest pain
  • Hallucinations
  • Ringing in the ears

Serious side effects of clonidine

The most serious side effects of clonidine include:

  • Low blood pressure
  • Fainting
  • Slow heart rate (bradycardia)
  • Heart block
  • Depression
  • Serious gastrointestinal problems such as GI block or ileus (spinal injections only)
  • Withdrawal symptoms
  • Rebound high blood pressure
  • Severe allergic reactions

Weight changes

Weight gain is a rare side effect of clonidine, occurring in less than one percent of people taking the drug. Clonidine also does not increase appetite, though animal trials show it may make rats eat more. People taking clonidine, however, have not reported increased eating, so it’s safe to say clonidine has little to no effect on appetite or weight. 

Hair loss

Hair loss is a very rare side effect of clonidine. Its estimated incidence is 1 in 500 patients. At that low of a rate, it’s uncertain if the drug is responsible. If clonidine does increase hair thinning, it will take a few months to be noticed. Talk to the prescribing healthcare provider if hair seems to be thinning. 

Sexual dysfunction

Clonidine interferes with sexual function, particularly in men. Libido decrease and erectile dysfunction are the most common problems, each affecting about 3% of patients taking clonidine. The rate of impotence, however, may be as high as 25%. While erectile dysfunction is generally a problem with blood pressure medications, clonidine and other drugs that widen blood vessels may be worse than others. Because sexual problems are a prominent reason men stop taking blood pressure drugs, it’s important to keep taking the medicine and tell the prescribing healthcare provider about the issue. Switching to other antihypertensive treatments could help fix the problem.

How soon do clonidine side effects start?

Some clonidine side effects can occur rapidly after the first dose, such as low blood pressure, slowed heart rate, itching, or allergic reactions. Most side effects, however, happen after one or more doses have been taken, including dry mouth, headache, drowsiness, and some serious side effects such as heart block. Other side effects can be delayed and take a few weeks or months of treatment before becoming an issue. These include anxiety, irritability, loss of appetite, and severe gastrointestinal problems. 

How long do clonidine side effects last?

Clonidine side effects, though commonly experienced, typically resolve when the drug is stopped. How long it will take for the side effects to fade will vary widely. For some people, it may take a day, while it may be a week or more for others. That’s how much variability there is in people’s ability to eliminate the drug. Side effects can last longer in those that have been taking clonidine for a longer duration of time. 

What are the long-term side effects of clonidine?

As a blood pressure or ADHD medication, clonidine is intended for long-term use. There are no side effects due to long-term use other than possible hair loss or weight gain, both of which are rare and may not be due to the drug. Many side effects will improve as the body adapts to the drug. Most will fade when the drug is stopped. 

Clonidine contraindications

Clonidine is contraindicated in anyone with known allergies to the drug. Clonidine injections are also prohibited in people with an active infection at the injection site or those with bleeding disorders or taking anticoagulants.

Pregnancy 

Though it’s not prohibited, women who are pregnant may want to avoid taking clonidine. Drug levels are high in the placenta and four times higher in amniotic fluid than in the woman’s blood. A healthcare professional may advise other blood pressure treatments.

Breastfeeding

Women who are breastfeeding are not prohibited from taking clonidine. However, no studies show that it’s safe for the baby. Clonidine is present in breast milk and theoretically could affect the child. Talk to the prescriber about the pros, cons, and alternatives to clonidine when nursing.

Children

Only clonidine extended-release tablets have been FDA approved for children, but only for ADHD. Transdermal patches are sometimes prescribed off-label to children, but this use is not proven to be safe or effective. The FDA has advised that children taking clonidine should be monitored for slow heart rate or low blood pressure.

Seniors

Because of declining kidney function, adults older than 65 years of age may not eliminate clonidine as efficiently as young adults. As a result, clonidine may build up to higher concentrations in the blood, raising the risk for side effects. In seniors, healthcare professionals will usually start with a lower dose and monitor for side effects during treatment. 

Clonidine warnings

As a drug that affects the central nervous system, clonidine carries a few risks. These risks may be more pronounced for some people.

Cautions

Some medical conditions could be worsened by clonidine. Others may make patients more vulnerable to side effects. These include: 

  • Kidney dysfunction: Declining kidney function slows the body’s elimination of clonidine and raises the risk of side effects.
  • Cardiovascular problems: Some heart or cerebrovascular problems can be worsened when clonidine is taken, including heart attack, coronary artery disease, stroke, heart failure, heart conduction problems, and heart block. People with low blood pressure, uncontrolled blood pressure, orthostatic hypotension, and problems with fainting will also require close monitoring when given clonidine.
  • Raynaud’s syndrome: Clonidine can worsen Raynaud’s syndrome.
  • Depression: Clonidine can worsen depression. 
  • Surgery: Because of its effects on the heart and blood pressure, clonidine should not be taken several hours before and after surgery.

Withdrawal

Although clonidine does not create a physical dependence, the abrupt discontinuation of the drug can precipitate withdrawal. It could be severe and cause strokes or even death. However, the most perilous withdrawal risk is rebound high blood pressure. Other symptoms of clonidine withdrawal include agitation, nervousness, headache, and tremor. Caregivers of children taking clonidine are advised to be especially wary. Children commonly have digestive system problems that can make them vomit up their dose, making them more likely to experience clonidine withdrawal.

Abuse

Clonidine is not considered to have a risk of drug abuse.

Overdose

Get emergency medical care or call a poison control center if too much clonidine is taken. The drug slows down the nervous system and, in high enough doses, produces serious problems such as low blood pressure, heart rate abnormalities, breathing problems, seizures, and coma. Children are particularly vulnerable to overdoses. 

Symptoms of an overdose occur rapidly, usually in a half hour to one hour after ingesting clonidine. They include:

  • Low blood pressure
  • Slowed heart rate
  • Slow and shallow breathing
  • Sleepiness
  • Fall in body temperature
  • Weakness
  • Slow reflexes

The maximum daily dose of clonidine is 2.4 grams per day for adults and 0.4 grams per day for children and adolescents. 

Clonidine interactions

Clonidine has several drug interactions. To understand them, remember that clonidine is a depressant. It slows down the nervous system, lowers blood pressure, slows the heart, and affects the conductivity of the nerves that power the heart. This means that clonidine must be used cautiously with other CNS depressants, blood pressure drugs, and drugs that slow the heart or alter its conductivity.

CNS depressants will worsen the depressant effects of clonidine. Besides sedation, depressants can also slow down the heart and breathing. Here’s a short list of CNS depressants that should be used in caution with clonidine:

Drugs that lower blood pressure will add to the blood pressure lowering effects of clonidine. There are many different types, but the most serious drug interactions are caused by blood pressure drugs that also slow down the heart, such as beta blockers and calcium channel blockers. 

Finally, drugs that affect heart rhythm and conductivity can potentially cause serious heart problems when taken with clonidine. These include:

How to avoid clonidine side effects

Most people will experience adverse effects when taking clonidine. Thankfully, they tend to be mild. Some rules-of-thumb can help minimize any problems.

1. Make sure the prescriber has a complete medical history

The most efficient way to prevent clonidine side effects is to tell the prescribing healthcare provider about every current and past health condition as well as all the prescription drugs, over-the-counter drugs, and dietary supplements being taken, especially:

  • Heart problems
  • Kidney disease
  • Depression
  • Raynaud’s phenomenon
  • Any alcohol use
  • Any use of sedatives, barbiturates, benzodiazepines, or other CNS depressants
  • Any use of heart medications
  • Blood pressure medications
  • Any upcoming surgeries
  • Pregnancy or any plans to become pregnant
  • Breastfeeding or any plans to breastfeed

2. Take clonidine as directed

Follow the instructions given by the prescriber or written on the prescription label. Do not take extra medicine.

3. Do not stop taking clonidine

Suddenly stopping clonidine could cause withdrawal side effects that range from unpleasant to life-threatening. If the drug is causing problems or side effects are intolerable, talk to the prescriber about quitting. Quitting may require taking a steadily decreasing dose over a span of a few days.

4. Get help if vomiting 

If vomiting is a problem, there’s a chance that the drug is being thrown up, too. That’s another cause of clonidine withdrawal. Call the prescriber if vomiting is interfering with taking the drug. This is especially important if the patient is a child. 

5. Stop drinking alcohol

Both alcohol and clonidine are depressants, so they will increase each other’s effects on drowsiness, dizziness, low blood pressure, fainting, and slowed breathing. 

6. Avoid medicines and supplements that cause drowsiness

If combining alcohol with clonidine is a problem, so are prescription drugs, over-the-counter medications, and supplements that are also depressants. These include drugs like sleeping pills and strong pain medications, but they also include popular over-the-counter drugs and supplements like antihistamines, melatonin, and “cold and flu” medications. 

How to treat side effects of clonidine

There will come a time when someone taking clonidine will have to manage side effects. Here’s how to do it.

Drowsiness and dizziness

If tired or dizzy, sit down. Stay seated until the attack passes. Don’t do risky things when overly tired or feeling dizzy. Driving, playing hazardous sports, operating machinery, or even chopping vegetables creates a risk for injury. Make sure to stand slowly as well. 

Dry mouth

Chew sugarless gum, eat sugarless candy, take frequent sips of water, or use a humidifier. If the problem gets too bad, the prescribing healthcare provider may have treatment options such as artificial saliva.

Vomiting

Immediately talk to a healthcare professional if vomiting occurs within half an hour of taking clonidine. Do not take a replacement dose until told to do so.

Erection problems

Get medical advice from the prescriber if getting and maintaining erections is a problem. There may be better alternatives for controlling blood pressure.

Slow or irregular heartbeats

If the heart is beating slowly or seems off, contact a healthcare professional.

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