Doctor only injected one side of her mouth with botox to see how much of an impact it had

This doctor was willing to forgo facial symmetry for a fortnight to prove the power of Botox.

Dr Bita Farrell has gone the extra mile to show what impact the aesthetic treatment can have on clients by volunteering to be her very own 'lab rat'.

Although you shouldn't take a leaf out of her book and give it a whirl yourself, Dr Farrell's before-and-after content can certainly give you a better idea of what to expect if you book in with a professional. Farrell is world-renowned aesthetic doctor, based in California, and she's previously injected one side of her face with Botox for 'the sake of science and education' to show what a difference it can make.

And Dr Farrell also decided to do this to her upper lip - in an area often referred to as lipstick, vertical or smoker's lines, and perioral wrinkles - to show how Botox works once again.

She carried out a cosmetic procedure commonly known as a 'lip flip', which involves relaxing the muscles around the mouth with the neurotoxic protein to give the appearance of a fuller upper lip.

Dr Farrell explains on her website, the Natural Aesthetics Center: "In the lip flip procedure, we carefully inject small amounts of Botox into your upper lip.

"As the muscle relaxes, the lip will curl upward, resulting in a fuller appearance. The lip flip gives your lips a subtle, but natural-looking feel."

So, she carried out a 'split-face experiment' where she only injected the left side of her face to show how impressive Botox can be if you want to 'soften' lines above your upper lip.

The medic told her 240,000 Instagram followers: "It also helps flip the lip out over itself to make it look fuller and it minimises the curling under of the lip when you smile.

"I'm only going to inject this side with one unit in each spot and we will come back in two weeks and you guys can see what it looks like."

Two weeks later, Dr Farrell recorded the second part of her video to show off the results, and the proof was in the pudding.

The side of her face where she had injected Botox into the upper lip area appeared visibly smoother, while the left half of her lip also seemed to be a lot more defined.

"This is the treated side," Dr Farrell explained. "You can already see that it's fuller and the cupids bow is a little bit higher on this side.

"The lip has flipped out on itself, it looks fuller and especially when I smile, it doesn't curl under. In addition, you can see that the smoker lines or lipstick lines on this side are much softer."

But she threw social media users for a spin when she captioned the post: "Which side do you prefer? I like the non-treated side more."

The split-face experiment left people divided in the comment section, but nobody could deny that it was impressive to watch.

Some people who have undergone lip flips shared their experiences too, warning that although it might look great, there are some drawbacks.

One person said: "You are awesome showing us this split view."

Another wrote: "I liked the treated side."

A third added: "You can't suck from a straw, it was the worst! It looked cute though."

A fourth wrote: "That is great! Thank you I have some of those lines so wondering if anything could be done."

While a fifth chimed in saying: "I'd rather have smoker lines."

Other aesthetic practitioners also shared their thoughts, with one saying the lip flip procedure was 'either a love or hate for people'.