Side effects of the Sphenopalatine Ganglion Block are almost always positive not negative. The most often cited effect is a feeling of calmness or peace. Many patients find that their tensions and anxiety drift away.
High blood pressure tends to stabilize and A-fib may improve.

Some patients describe an effect feeling energized and prefer to self administer after wakening while others feel a sense of calm and liketo do it in the evening prior to sleep.

While the SPG Block turns of the Sympathetic “Fight or Flight” reflex and turns on the Parasympathetic “Feed and Breed” or “Eat and Digest” reflex it does not seem to stimulate weight gain in fact in general has the opposite effect possibly by eliminating nervous or stress eating.

Women tend to have a positive effect on their libido , sometimes very soon after administration and some Aorgasmic women have reported developing normal or heightened sexual release.  More on the topic of Female libido and SPG Blocks.

Most of the side effects are positive and their are literally hundreds of stories unexpected positive side effects. Frequently, I will use SPG Blocks on patients for their side effects. They seem to work to decrease phobias and can be used prior to flying, public speaking or other anxiety producing events.

Local side effects can vary by mode of administration. The Supra-Zygomatic injecton approach can rarely result in slight bruising but this is rare. Some patients have felt a very brief period of light headedness after a Supra-Zygomatic SPG Block.

The trans-nasal approach with the Sphenocath can allow anesthetic to drip into mouth or throat with bitter taste and temporary numbness. Occasionally, there can be slight nasal irritation or a speck of bleeding after use of Sphenocath. The cotton tipped nasal catheters will see this effect more often.

All SPG Blocks tend to increase sinus drainage initially but decrease chronic sinus issues over time. Chronic sinusitis/ rhinitis seem to improve over time in many patients.

The intra-oral injection can be uncomfortable when passing thru palatal tissues, this can be avoided with topical anesthetic followed by slow injection of just a drop or two of anesthetic and waiting for it to take effect before doing the injection through the greater palatine foramen.

All SPG techniques can cause numbness of the upper teeth, maxilla, cheeks and lips but i is rarely a problem. This is most likely to occur with the intra-oral approach.

Many of the side effects such as reduction of anxiety and/or depression are so common that SPG Blocks are given precisely for the side effects.

A recent discovery that may prove to be extremely important to millions of patients is that Sphenopalatine Ganglion Blocks eliminate Essentia Hypertension in about one third of patients.  A new article was published in 2018.