Is supplement's harmful to health?

Depends on the supplements and where they come from. Best to see your Doctor first to see if you really need some or not. Then only buy quality well known name brands. I take a few and I only buy the best I can. They are only harmful if you really don't need them or you buy them from unknown online stores. See your Doctor first!

I personally believe that supplements are not bad for your health, they can be good when used responsibly.  Like any drug, over dosage tends to not be such a good thing...

Typically, they are created to enhance health and MUST be taken properly. Overdosing on them is definitely bad for health. There  is a scale of good and bad quality products. The Cheap grocery store variety  products are a waste of money in comparison  to higher quality products that reputable health enhancement stores would offer.

your question needs to be more specific as to what kind of supplements but overall, they aren't bad for you if you don't overdo it. anything can be harmful if you abuse it (even drinking too much water)

Yes. Espicially if you take too much.

It depends on the supplement, how much, and if it can interfere with any medications you may be taking. The only thing I take is something for my allergies, and that is as needed. So when my bloodwork showed a deficiency in vitamin D, my doctor suggested I take a supplement.

My dad has heart disease and takes warfarin. He cannot take CoQ10 because it can decrease the effectiveness of it. He also cannot take cranberry supplements, or drink cranberry juice, because it can increase the effects of it. Either can be deadly.

And as for those weight loss supplements? My husband has tried two different ones. He ended up in the hospital both times for what they suspected was a heart attack. Some of the ingredients are 5 times the recommended daily allowance. Thankfully there was no heart attack, but he still had to sty for 2-3 days until it was flushed from his system and they checked to make sure no permanent damage was done.

If supplements were bad for health, they would be banned. But in facts many people still use them every day. The point is how you use them.

As someone who relies on supplements for important nutrients a plant based diet just can't give, I back them up fully. BUT: Consulting a doctor to see what could be helpful for your body and what you could benefit from is always a must. Supplements normally aren't checked by the FDA, so the claims the company slaps on the bottle could be completely false or exaggerated  (weight loss fad supplements are a great example of that)