A galactagogue is a drug, a food or an herb that increases milk supply. The popular herbs are the following:

Fenugreek is a middle-eastern spice, oldest medicinal herbs known. It is usually used with blessed thistle. Blessed thistle is traditionally used for loss of appetite and indigestion. It is not recommended during pregnancy. Both may cause allergic reactions and must be taken with precautions.
Goat's rue is a plant native to Middle East and Europe. It has been used to  lower blood sugar levels and treat tuberculosis. Women also use it as a galactagogue. It is a member of the pea family of plants which includes soybean, alfaalfa, peanuts and fenugreek. Check with your doctor if you have sensitivity or allergy to this nature.
Shatavari, or wild asparagus, has been used for hormonal support, stomach issues and is widely used for increasing milk in India.  It has antioxidant properties which help improve the overall health of the nursing mom. Shatavari is a diuretic and is oily in nature.  Avoid taking Shatavari if you have issues like congestion. Also, this herb contains plant oestrogens, it can affect women who have oestrogen sensitivity. It could cause weight gain and breast enlargement or tenderness. 
Fennel or fennel seeds is known to increase breast milk supply and it can even provide many health benefits to the baby. Fennel may be considered safe while breastfeeding, but it can be dangerous during pregnancy.
Alfalfa contains phytoestrogens or plant-estrogens, which can increase breast tissue and milk production. It is an herb that has been used as a medicine for many years.  Like all other herbs, Alfalfa is generally safe when taken in moderation. Check further its connections with  auto-immune disorders.

Moringa oleifera is a plant, a vegetable that is also called the miracle tree, drumstick tree, or the horseradish tree. Moringa is a superfood which also helps in making more breast milk that has been used for centuries due to its medicinal properties and health benefits. As a galactagogue, our premium moringa is safe to be taken by ante-partum & post-partum moms. It is 100% vegan and does not go through any extraction or artificial process. The best herbal lactation supplements are those that are organic, pure and has other proven health benefits not just for the mom, but also for the baby like Golacta.

Disclaimer

These information were gathered to the best of our knowledge. However, it must not be used as sole source of information. Breastfeeding is highly individualized and must be discussed in person with a lactation consultant.