I m using sustanon 250, winstrol and oxandrolone for 6 weeks. will it shut down my natural testosterone production. should i use tamoxifen after cycle?

Yes: All Anabolic steroids will suppress lh in your pituitary gland and therefore reduce your natural testosterone production to castrate levels. Tamoxifen is a estrogen receptor blocker. Since you won't be making your own testosterone for 4-6 weeks post cycle, you'll have no estrogen to block. Don't mess around with these drugs; they'll make you infertile, shrink your nuts and you'll need them 4ever.

Anabolic steroids: All three of these drugs are Anabolic steroids and will shut down your own natural testosterone production, as well as sperm production, likely causing infertility. Taking tamoxifen will not change this. These drugs are illegal if used for athletic enhancement, can have significant long term side effects. You are a young male who should not be sacrificing your future for some short term gain.