Are there truly any worthwhile shampoos on the market to maintain/combat hair thinning? i've heard various opinions on this matter.

Hair: Generally should use pH balanced shampoos and conditioners (in acidic range). Peroxide can do serious damage to hair. Could have TSH level checked.

Alopecia?: There is a condition called alopecia which causes the hair to fall out. This is different from male pattern baldness which is genetic and not a disorder. A dermatologist can tell you if you have alopecia (an autoimmune disorder) and treat it. Shampoos don't help. Stay neat & clean and be a decent person. This is more attractive than hair. Peace and good health.

Claims not proven: You will hear quotes from a few individuals of hair growing back with certain shampoos packaged along with other products but there is no scientific proof that any of them works. Even Rogaine, which is a medication and not a shampoo, is only minimally effective for some. The only thing which appears to grow is the pocket book of the manufacturers.