I've been taking OTC Zyrtec daily for about 10 months for year-round allergy symptoms. Not only does it not work great on my itchy eyes and nose, I've gained weight, I'm tired all the time no matter how much sleep I get, I'm fatigued and have constant muscle weakness, I'm irritable, my blood pressure has gone up drastically to the point I started BP meds last week, I'm having weird dreams...it got to the point my doctor tested my thyroid function because my list of symptoms fit hypothyroidism all the way down the line. My thyroid test was normal - on the low end, actually. I started researching what else could cause my symptoms and stumbled across this forum. I won't be taking Zyrtec again and hope I feel more like the old me in a couple of days. Thanks to all of you who posted your side effects - it is such a comfort to know I'm not really losing my mind and this drug may be causing my problems!

Zyrtec took pretty good care of my itchy, watery eyes, but after a short time I was having a difficult time getting to sleep--unusual for me. It would take up to 2 hours to fall asleep and I would be exhausted in the morning and irritable during the day. At night I had wild dreams like nothing I've ever had before. Finally decided one weekend to quit the Zyrtec. My normal sleep pattern came back immediately, no crazy dreams, and I've got some of my energy back. Sorry it had the adverse effects on me because it was good relief for my allergy symptoms.

I have numerous allergies, including an allergy to milk. I just discovered that ZYRTEC contains "lactose monohydrate" which is MILK! If you have a milk allergy or are lactose intolerant, beware!

I started taking this medication in 1996 for allergies and itchiness. I have tried many times to stop taking it and after 3 days develop severe itching and burning particularly on my hands, feet and scalp. I thought it was my allergies acting up and started taking it again. I have since learned that this is a form of withdrawal from this medication. I am very upset that I ever started taking it, as I don't know how I am going to quit. It is really too painful to try and stop. I am not the only one who has experience this reaction. Now that is over the counter it scares me. Beware!!

I took Zyrtec because I thought I was having severe hayfever. For the past 2 days, I've taken it, I've been waking every 2 hours and having severe extreme tiredness and extreme nightmares. So bad that I made a note to check online, during 1 of the awake times. Just today, I have had 3 severe dreams that I can recall completely. I normally don't dream or recall that I dreamed, so these nightmares really stood out because of the violence, weirdness, and helplessness I felt in them. After reading several posts, I see I'm not alone when it comes to "nightmare side effects". I'm almost 39, and having bad nightmares with 1 pill per day for last 2 days. What's it doing to my son who's 17 and been using it off and on for the past year? All those times I forced him to take his meds. and even now recall he had complained about nightmares, I just didn't know it was the pills.

I have been taking a Zyrtec every night for years. I have both outdoor seasonal allergies, as well as indoor allergies - and Zyrtec works great for both without making me drowsy! I love this product!!!

I took Zytrec for 7 years. It worked great! No hives and no hay fever. After about 4 or 5 years I started having some very vivid and terrifying dreams and nightmares; most of these involved killing people (about 2 or 3 times a night). I was kind of stuck because none of the other medicines had done anything for my hives (Claritin and Allegra). I finally had to stop taking Zyrtec because in one dream where I was in a fight, I actually swung my arm and punched my wife in the nose. Afterwards I went online to search for these type of side effects to the drugs and read that some people were saying that Zyrtec contributed to or created nightmares and even made your allergies worse! They said that the drug made you very dependent on it. Finally after two years on the drug, I went to the doctor and changed to Claritin. Now I only take 1 Claritin once a week versus 1 Zyrtec every day and there are no nightmares! Zyrtec worked great at doing what it was supposed to do, but the side effects were not worth the cause. I also concur that Zyrtec makes your allergies worse. I took it mainly for my hives. After 26 hours of taking my medicine, I would get hives. Like clockwork. How is it now that I am able to go a week with no bad outbreaks and no nightmares? Coincidence? Be careful with Zytrec, I'm worried because it is now an over-the-counter drug.