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^Sang GW. Pharmacodynamic effects of once-a-month combined injectable contraceptives. Contraception. April 1994, 49 (4): 361–385. PMID 8013220. doi:10.1016/0010-7824(94)90033-7. The exact formulation and the size of the microcrystals is most important for duration of action. The smaller particles are more rapidly dissolved than larger ones and, hence, MPA appears more rapidly in the circulation, with more rapid elimination from the body. This is also true for the once-a-month formulation, Cyclofem. From our laboratory’s data, the distribution of particle size of Cyclofem is showed in Table 2. [...] TABLE 2. Distribution of particle size of crystalline steroids in Cyclofem (aqueous suspension). Size of particle (μm): ≤4: 0.3%. 5–6: 7.3%. 6–8: 16.7%. 8–10: 29.0%. 10–13: 29.7%. 13–16: 9.9%. 16–20: 0.5%. >20: 0.1%.
^Coutinho EM, Carlos de Souza J. Conception control by monthly injections of medroxyprogesterone suspension and long-acting oestrogen. Journal of Reproduction and Fertility. March 1968, 15 (2): 209–214. PMID 5643482. S2CID 37979625. doi:10.1530/jrf.0.0150209.
^Oriowo MA, Landgren BM, Stenström B, Diczfalusy E. A comparison of the pharmacokinetic properties of three estradiol esters. Contraception. April 1980, 21 (4): 415–424. PMID 7389356. doi:10.1016/S0010-7824(80)80018-7.
^Koetsawang S. Once-a-month injectable contraceptives: efficacy and reasons for discontinuation. Contraception. April 1994, 49 (4): 387–398. PMID 8013221. doi:10.1016/0010-7824(94)90034-5.
^Sweetman SC (编). Sex hormones and their modulators. Martindale: The Complete Drug Reference 36th. London: Pharmaceutical Press. 2009: 2082. ISBN 978-0-85369-840-1.
Note: Though not listed here, many anabolic steroids can also be estrogenic as they can be aromatized into estrogen-like metabolites that possess estrogenic activity.