In women, the use of combined birth control pills can improve acne. These medications contain an estrogen and a progestin. They work by decreasing the production of androgen hormones by the ovaries and by decreasing the free and hence biologically active fractions of androgens, resulting in lowered skin production of sebum and consequently reduce acne severity. First-generation progestins such as norethindrone and norgestrel have androgenic properties and may worsen acne. Although oral estrogens decrease IGF-1 levels in some situations, which could theoretically improve acne symptoms, combined birth control pills do not appear to affect IGF-1 levels in fertile women. Cyproterone acetate-containing birth control pills seem to decrease total and free IGF-1 levels. Combinations containing third- or fourth-generation progestins, including desogestrel, dienogest, drospirenone, or norgestimate, as well as birth control pills containing cyproterone acetate or chlormadinone acetate, are preferred for women with acne due to their stronger antiandrogenic effects. Studies have shown a 40 to 70% reduction in acne lesions with combined birth control pills. A 2014 review found that oral antibiotics appear to be somewhat more effective than birth control pills at reducing the number of inflammatory acne lesions at three months. However, the two therapies are approximately equal in efficacy at six months for decreasing the number of inflammatory, non-inflammatory, and total acne lesions. The authors of the analysis suggested that birth control pills may be a preferred first-line acne treatment, over oral antibiotics, in certain women due to similar efficacy at six months and a lack of associated antibiotic resistance. Progestogen-only birth control with androgenic progestins has been associated with worsened acne.