Herbs are drugs (medicines), and yes, you can easily overdose. Long-term medicinal usage of herbs is not usually recommended.

I suggest you put your question to a qualified herbalist, stating why you are taking these herbs.

You need to be very careful, especially with the St. John's Wort, which can interfere with a lot of other herbs and conventional medications, and which should never be taken for long periods. It should be used strictly under professional supervision.

Expert supervision is also recommended for Evening Primrose oil. Ditto for Black Cohosh. And 2-3 leaves is the recommended dosage for Feverfew.

My advice generally is NOT to take herbal medicines without checking first with an expert - not later, which may be too late! Use herbs with the same caution as you'd use prescription medications. You need to have a professional diagnosis of your problems, an appropriate treatment regime, a dosage to suit you, and to eliminate the possiblity of interactions with other drugs/herbs, and be aware of contraindications.

Here is a link that might be useful: herbalists

Omilord yes! It's possible to take too much of anything! People forget that herbal supplements are drugs, with side affects... some which you can't see, for example liver damage. Since a lot of herbal supplements haven't been studied for side affects, some you might never know. If you have to take a lot of something, I think it is safe to say it's not working for you. AND if that's not the situation, just cuz a little works, doesn't mean a lot is better.

Thank you for the advice. I'm not taking more than the recommended amount on the back of the bottles. But I've been taking St. John's wort all fall and winter and will discontinue taking it for now, as it makes me sensitive to the sun. I've been taking the Feverfew continually for 2 years. I better make an appointment with an herbalist then, that is if I can find one.

What are you taking the supplements for? Sometimes you can find one or two things, or a patent formula, that does everything you want it to do without going through all this.

The Feverfew makes my monthly migraines less painful and less frequent, it also seems to help with osteoarthritis.
St. John's wort for mild depression, with marked improvement.
Primrose Oil stops painful breasts that I have 2 weeks before my period.
I would like to begin taking Black Cohosh for perimenopausal smptoms.