- DOO GRO Hair Vitalizer Mega Thick 4oz DOO GRO Hair Vitalizer Mega Thick Anti-Thinning Formula helps thicken and strengthen weak and damaged hair. Its special blend of vitamins, pure herbs, shea butter and botanical thickeners provides needed nourishment for strong, healthy, growing hair. Safe to use on all types of hair including natural, color treated, and relaxed. Works wonders on thinning edges and temple areas.