You may want to read this study that shows no difference in efficacy with the two routes of administration:
Bioavailability of hCG after intramuscular or subcutaneous injection in obese and non‐obese women
The study above found that IM was more effective than sub cutaneous in women. Below other studies show that both modes of injection are equivalent.
Jones, T. H., J. F. Darne, et al. (1994). "Diurnal rhythm of testosterone induced by human chorionic gonadotrophin (hCG) therapy in isolated hypogonadotrophic hypogonadism: a comparison between subcutaneous and intramuscular hCG administration." Eur J Endocrinol 131(2): 173-8.
When human chorionic gonadotrophin (hCG) is used to stimulate testosterone synthesis and release in males with hypogonadotrophic hypogonadism, it is administered two or three times weekly by intramuscular injection. We have compared the pharmacokinetics of a twice weekly standard dose of hCG (5000 U) given for the first week by intramuscular injection and in the second week by self-administered subcutaneous injection. The patients studied had Kallmann's syndrome, isolated idiopathic hypogonadotrophic hypogonadism or post-traumatic isolated hypogonadotrophic hypogonadism. Salivary testosterone was collected twice daily at 08.00 h and 20.00 h, and serum testosterone was collected after 0, 24 h, 72 h, 120 h and 168 h each week. The cumulated serum and salivary testosterone levels were comparable on both intramuscular and subcutaneous hCG. In normal males there is diurnal variation in testosterone, with peak serum levels in the morning falling to a nadir in the evening. The exact nature and controlling factors of this circadian rhythm have not been established. In four of the subjects, the twice weekly hCG injections, either subcutaneous or intramuscular, produced a regular testosterone diurnal rhythm. The other four patients had fluctuations in testosterone but with no strict diurnal pattern. This study provides evidence that the luteinizing hormone-like action of hCG is necessary to prime the circadian rhythm but only a single bolus of hCG is sufficient to induce the rhythm in the absence of endogenous gonadotrophin production
. In conclusion, self-administered subcutaneous hCG is safe and produces comparable levels of serum and salivary testosterone to that administered by the intramuscular route. Moreover, it was very well accepted by the patients and was preferred to conventional treatments. Human hCG in some patients with hypogonadotrophic hypogonadism produces normal physiological changes in daily testosterone levels.
Saal, W., H. J. Glowania, et al. (1991). "Pharmacodynamics and pharmacokinetics after subcutaneous and intramuscular injection of human chorionic gonadotropin." Fertil Steril 56(2): 225-9.
OBJECTIVE: The pharmacokinetics and efficiency of human chorionic gonadotropin (hCG) after subcutaneous (SC) injection was to clarify in comparison with the intramuscular (IM) mode of administration. DESIGN: In a prospective study, the pharmacokinetics of hCG and the response of serum testosterone (T), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) after an IM and SC injection of 5,000 IU hCG were evaluated up to 144 hours in two randomized groups. SETTING: The study was carried out in a clinical dermatology department providing tertiary care. PARTICIPANTS: Twenty-four healthy male volunteers with a mean age of 22.7 +/- 4.3 years were divided into two groups. INTERVENTIONS: Human chorionic gonadotropin (5,000 IU) was injected IM or SC. MAIN OUTCOME MEASURE: Serum concentration of /b-hCG, T, LH, and FSH were evaluated after IM and SC administration of hCG. Differences between the two groups were determined by t-test. RESULTS: Compared with IM administration of hCG, peak serum drug concentration was significantly delayed (P = 0.01) and serum half-life was prolonged (P = 0.01) after SC injection; however, T, LH, and FSH responses were identical. CONCLUSIONS:
Subcutaneous application of 5,000 IU hCG is as effective as IM administration in terms of steroidogenesis.
In my own personal bias, I think IM is better. That is why I use a shallow IM injection:
Video: How to Use HCG with Testosterone To Preserve Fertility, Libido and Testicle Size
