Senna (Cassia senna syn. Senna alexandrina)is a tropical flowering plant with hundreds of subspecies or variations. The senna leaf is pinnate, or wing-like, similar to a fern with yellow flowers and, since it’s a legume (in the bean family), the plant contains a pod of seeds. 
Between the powerful laxative effect and the lack of solids in your system, you can pretty much figure out how this is going to progress.
There are over 400 species of Cassia. Most are indigenous to North, Central, and South America, and Africa; but it is now found in tropical and subtropical regions of all continents, except Europe. … All ancient cultures, including the Aztecs, Asians, and Africans have used infusions of the Cassia species as a laxative. It is still an ingredient in several over-the-counter laxatives. The first records show the herb being used medicinally by Arabian physicians in the 9th century CE, and has always been used for constipation. … Senna was given the name of Purging Cassia in Europe during the Middle Ages because it was used at that time in an Italian medical school as a purgative. 
Simply put, it unbinds stool, making it easier to have a bowel movement.
Today senna is also commonly referred to as cassia. Extracts from the seeds and flowers are used in different formulations including senna tablets. And senna tea is brewed from senna leaves and flowers. First used commercially in the U.S. after WWII, the active ingredient is called senna glycoside (sennosides) which when it meets the intestines and colon, starts to do its work; speeding up the process of churning and then, emptying the bowels. The side effect is gas and bloating while this is happening, and that’s the single most complained-about side effect of a senna-based laxative.
It’s also important to note that the American Herbal Products Association (AHPA) cautioned the leaf used long-term can be dicey, but has given no such warning for the fruit. 
The big question is, does senna work for weight loss?
Usually senna is combined with other ingredients as a weight loss supplement to do the dirty work—getting the crap out.
Take Dr. Tobias Colon: 14-Day Quick Cleanse, packed with senna, which claims to “support detox, weight loss and increased energy levels.” Dr. Tobias Colon tablets (14-day supply) costs $12.32 on Amazon.com, and between $15-$29 across the web.   
But for the purposes of this review, there is no evidence senna is in any way effective for weight loss.
Another popular senna-based weight loss product is Laci Le Beau Super Dieter’s Tea. It boasts,
“…a unique combination of premium herbs and spices, including senna, an herb with a history of traditional use that promotes healthy digestion and helps support weight loss. All natural and caffeine free, this herbal tea also helps you eliminate your body’s impurities. When combined with a healthy, reduced-calorie diet and fitness plan, Laci Le Beau Super Dieter’s Teas have shown to support your weight-loss efforts.” back to menu ↑
There’s not much to this one; simply drink the tea or take the tablets for a week or so with a basic “cleanse” diet, usually liquids only (one version is called a “juice fast”). Between the powerful laxative effect and the lack of solids in your system, you can pretty much figure out how this is going to progress. Then simply reintroduce yourself to healthy foods, starting with soups and working your way back to solids. But it’s not a long-term diet; in fact, there are some serious side effects to taking strong laxatives. We’ll look at those momentarily.back to menu ↑
The Science (or Lack Thereof) Behind Senna
According to researchers, there’s simply no evidence senna helps you lose weight. The Food and Drug Administration (FDA) has drug-approved senna as a laxative for constipation. The other use is to help clear the gut before a colonoscopy. That’s all. 
According to the federal government’s National Library of Medicine, senna is “likely effective” for constipation when used with a stool softener like psyllium (think Metamucil). And that’s it. Far more evidence is needed to rate the effectiveness for weight loss, researchers say. 
The National Institutes of Health (NIH) medicine online database, MedlinePlus.gov, says that senna may be “possibly effective for bowel preparation before colonoscopy,” though good old fashioned castor oil (ask your mom or grandmother) does essentially the same bowel cleaning. 
But for the purposes of this review, there is no evidence senna is in any way effective for weight loss. But this hasn’t stopped marketers to tout its effectiveness or stopped people from taking it regularly.
Long-term use may affect electrolyte balance, which can lead to heart function disorders, muscle weakness, liver damage, and other harmful effects. And, NIH says, it can lead to a potassium deficiency when over-used. And lots worse, especially when taken with water pills (diuretics), which apparently is a frequent combination for people seeking very quick—but very unsafe—extreme weight loss. And liver damage has been seen in people who abuse senna for weight loss.  
The AHPA warns that people with abdominal pain, diarrhea, or pregnant or nursing moms not use senna and, importantly, states quite clearly that any product containing senna or cassia include this warning: “Not for long-term use.” back to menu ↑
Word on the Street About Senna
How do you counter nearly ten thousand positive reviews and a “best seller” tag at Amazon? Dr. Tobias’ senna-based “14 Day Quick Cleanse to Support Detox, Weight Loss & Increased Energy Levels” couples the laxative with probiotics, psyllium husk and flax seed. People are surprised, shocked even, by what is evacuated from the colon after the cleanse. But again, what about weight loss? One customer said that while the product flushed out their body, it inspired them to eat healthier and after doing the senna cleanse they felt “lighter.” 
So we take that as a no; there’s no weight loss save the junk flushed from your colon. Like that Big Mac from 2009.
The Laci Le Beau Super Dieter’s Tea, also featuring senna as the main ingredient, is also very popular on Amazon, with 4.3 stars from more than 150 reviewers. And here, people claim they have lost weight with the tea, with diet and exercise! 
Reviewer “Tazrin” (2015, 5 stars) says, “Awesome! I lost 5 lbs in the first week just from drinking this and making minimal changes to my diet and exercise regimen. Combined with a good diet and workout program, this will remove all bloating and discomfort and will cleanse you out if you have a bad cheat meal! I highly recommend it.” 
On the Laci Le Beau Super Dieter’s Tea website, reviewer “Dori M.” of Newnan, Georgia says the tea is
“…totally great!!! I love that the product is all natural and truly works. At 41 years old, I have to work at my weight more than ever and this product helps support my weight loss efforts. In addition to eating right, I exercise 30 minutes at least 4 days a week. I used the product as directed and saw results within a week. Thanks so very much for a great product.” 
This review makes the point rather succinctly, if perhaps unintended—this tea is a tea; the weight loss comes from “eating right” and regular exercise. Period.
The most interesting review on the Dieter’s Tea comes from “Mary” (2017, 5 stars), who claims to have been drinking this tea for decades:
I’ve been drinking LLB almost every night for the past 25 years. I’ve had chronic constipation since I was an infant and was diagnosed with slow colon. This is a non-medical option that helps keep me “regular”. Yes, I know that goes against the manufactures directions, but it’s the ONLY thing that works for me. When I was pregnant, I was told to stop drinking it. After a week of no “movement”, eating lots of fruits, veges, fiber and drinking tons of water, still nothing. A gallon of prune juice (hey, I was DESPERATE), still nothing. Finally, my doc said, “drink the tea.” My daughter was 9lbs, 6 oz and perfectly healthy. If you’re looking for a fast weight loss option, make no mistake—you will drop pounds of waste as this stuff can make you crap your pants if you’re not used to it or overdo it. I would, however, suggest eating healthy, exercising and all the other stuff your doctor tells you. If you need relief from occasional constipation and bloat, this stuff is the ticket. 
Well, there you go. It’s a laxative. Nothing more.back to menu ↑
The Bottom Line: Is Senna Worth a Try?
For weight loss: Risky. For constipation: Worth a Try. No pun intended here, but the real bottom line is this: when used for occasional constipation, senna is great. Any other use is ineffective, and in the case of overuse or long-term use (beyond a week or two) may be dangerous to your health. And, there’s virtually no scientific evidence that senna contributes to weight loss besides the technical ‘weight’ lost after a bowel movement. Which, of course, shall return sure as the sun will rise tomorrow.