American College of Obstetricians and Gynecologists’ Breastfeeding Expert Work Group states, “galactagogues should not be considered a first-line therapy because current research on the effectiveness of pharmaceutical and herbal galactagogues is relatively inconclusive and all substances have potential adverse effects.” 
The Academy of Breastfeeding Medicine (ABM) does not recommend any specific galactagogues. They developed a clinical protocol that details stepwise management for insufficient milk production in lactating patients. Nursing mothers should first be screened for pregnancy, medications, primary mammary glandular insufficiency, breast surgery, polycystic ovarian syndrome, hypothyroidism, retained placenta, ingestion of placenta capsules, theca lutein cyst, loss of prolactin secretion following postpartum hemorrhage, heavy smoking or alcohol use. In addition, low-weight infants should be screened to rule out other causes than poor feeding. Next, ensure that the expressing technique and any breast pumps used are effective as galactagogues will not increase the milk supply if there is infrequent or inadequate breast drainage. If clinicians recommend galactagogues they should ensure the patient is aware of medication timing, duration, and potential adverse effects. 
The majority of the study of galactagogues is in domperidone. However, per the FDA, "domperidone is not currently a legally marketed human drug and it is not approved for sale in the U.S. On June 7, 2004, FDA issued a public warning that distributing any domperidone-containing products is illegal." They cite risks of cardiac arrhythmias, cardiac arrest, and sudden death associated with domperidone as rationale. 
A 2020 Cochrane review identified and analyzed randomized controlled trials of pharmacologic and natural galactagogues to stimulate lactation in mothers. From their search, the pharmacologic regimens consisted of domperidone, metoclopramide, sulpiride, and thyrotropin-releasing hormone. Three studies reported improved milk volume (domperidone, metoclopramide, and sulpiride), and one reported weight gain in infants from receiving mother's milk (metoclopramide); however, these results were limited by a low quality of evidence. 
Supplemental/natural galactagogues identified for the meta-analysis included banana flower, fennel, fenugreek, ginger, ixbut, levant cotton, moringa, palm dates, pork knuckle, shatavari, silymarin, torbangun leaves, or other natural mixtures. The overall results observed benefit or little to no difference for improving milk volume. Adverse events were limited but consisted of minor complaints in mother and infant. Ultimately, the benefit of galactagogues for breastfeeding mothers is uncertain as the data were extremely limited, of low quality, and heterogeneous.