Hello. So, I bought peppermint plant already in pot from local store and about 3-4 weeks in it's leaves started to have brownish/black spots. At first they were little, not too much, I removed those leaves, but now there are not leave without them.
The question is - what is it and are those leaves are safe to use, for example, for tea?
More info - I haven't reported it, it's in pot with drainage, I water it about 3 times in week, it stands on window sill and gets about 3 to 4 hours of direct sunlight in evening.
Ouh, and it's flowering.

Hmm. It looks like some sort of fungal infection. I've had similar spots on my basil and peppermint before. What I did was make a baking soda spray, and I sprayed the plants, and then removed the infected leaves. Haven't noticed any issues since then. Maybe cut back on the watering a bit?

Also, I'm not sure about the safety of eating the leaves/using them for tea...

So I have an update. I did not gave up on this plant and its wonderful now. The bad leaves ar gone, as are the stems were they were growing, cuz new ones, much ticker came out and the leaves seem much greener and thicker also. What I change was bassicly nothing. When I noticed, that it is growing new stems, I changed the plants location - now its growing on balcony in almost full days sun.
I guess it was just some kinda natural cycle that it was going through.
Anyways - never give up on ya little plant buddies.