The most common side effects of clonidine are dry mouth, drowsiness, dizziness, and constipation. You may experience dizziness if you get up suddenly while using clonidine. 5. How to store Clonidine Hydrochloride 25 microgram Tablets Keep out of the sight and reach of children. Do not use Clonidine Hydrochloride 25 microgram Tablets after the expiry which is stated on the blister What other drugs will affect clonidine? Taking this medicine with other drugs that make you sleepy can worsen this effect. Ask your doctor before taking clonidine with a sleeping pill, narcotic pain medicine, muscle relaxer, or medicine for anxiety, depression, or seizures. In addition to its desired action, this medication may cause some side effects, notably: it may cause dryness of the mouth; it may cause constipation -- to prevent this, drink plenty of water or juice, and eat more dietary fibre; Clonidine hydrochloride is a centrally acting alpha-agonist hypotensive agent available as tablets for oral administration in three dosage strengths: 0.1 mg, 0.2 mg and 0.3 mg. Clonidine oral tablet can cause drowsiness. However, this effect might go away the longer you take it. It can also cause other side effects. More common side effects Clonidine comes as a tablet and an extended-release (long-acting) tablet to take by mouth. The tablet is usually taken two times a day at evenly spaced intervals. Transdermal clonidine comes as a patch to apply to the skin. It is usually applied to the skin every 7 days. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. How to use Clonidine Hcl ER. Read the Patient Information Leaflet if available from your pharmacist before you start taking clonidine and each time you get a refill. Initially, apply one Catapres TTS-1 (delivers 0.1 mg/24 hours) patch to an intact area of hairless skin on the upper arm or torso, once every 7 days.