Known brand names include Catapres.
A blood pressure pill that acts in the brain to turn down the nerve signals that tighten blood vessels and speed the heart. It treats high blood pressure, and stopping it suddenly can make blood pressure shoot back up.
Clonidine stimulates alpha receptors in the brain stem, at the base of the brain. That turns down the stress signals the brain sends through the nerves to the heart and blood vessels. As a result, blood vessels relax, the heart beats more slowly, and blood pressure falls. Blood flow to the kidneys and their filtering stay about the same.
Taken by mouth, it starts lowering blood pressure within 30 to 60 minutes, with the biggest drop within 2 to 4 hours. Dry mouth, drowsiness, and dizziness are common, and alcohol or other sedating drugs add to the sleepiness. If it is stopped suddenly, the body's stress chemicals surge, and blood pressure can climb fast along with nervousness, headache, and shakiness. Its calming effect on the heart's electrical system can also cause a very slow heartbeat, mainly in people with rhythm problems or who take other drugs that slow the heart.
Clonidine treats high blood pressure. Left untreated, high blood pressure can harm the brain, heart, blood vessels, and kidneys, raising the chance of heart attack, stroke, heart failure, kidney failure, and vision loss. It brings blood pressure down by slowing the heart rate and letting blood vessels relax so blood flows more easily.
The tablets are taken by mouth, either alone or with other blood pressure medicines. Healthy habits such as eating less salt and fat, keeping a healthy weight, exercising, and not smoking help control blood pressure alongside it. It controls high blood pressure without curing it, so people keep taking it even when they feel well and never stop it suddenly. Its safety and effectiveness in children have not been established in well-controlled studies.
Dry mouth is the most common effect, followed by drowsiness, dizziness, constipation, and sedation, and these tend to ease with continued use. Some people notice tiredness, headache, dry eyes, nausea, or sexual problems. The label treats stopping suddenly as dangerous, because blood pressure can rebound sharply and, rarely, lead to stroke or death. A very slow heartbeat, heart block, fainting, and allergic reactions with swelling can also occur.