In the Fall of 2018, United Therapeutics (UTHR) and MannKind (MNKD) announced a deal for a "secret molecule" for PAH which would have MannKind doing some concept formulation work. Upon completion of that formulation work, United Therapeutics would make a decision on whether or not to move forward. If United does decide to move forward, two $15 million milestones and low double digit royalties (if FDA approved) would be on the table. What triggers the earnings of those milestones has not been disclosed by either company. Subsequent to the United and MannKind deal being announced, United Therapeutics had an interesting slide on the pipeline section of its website which likely gave a very large hint that the "secret molecule" was Adcirca (Tadalafil). At the time, I wrote an article speculating this fact, titled, "United Therapeutics Looks To Develop Inhaled Adcirca - A Deeper Look".tadalafil powder
The evidence strongly points to the "secret molecule" being Tadalafil:

The term "inhaled DPI" - stands for "Dry Powder Inhaler"
The only dry powder inhaler deal United Therapeutics has is with MannKind
PDE5 is a specific class of drug. The only PDE5 drug United Therapeutics has in its platform is Adcirca (which is Tadalafil)
The time-line of "medium-term launches" jives with the timing it would take to do the necessary formulation work and studies
Tadalafil is owned and controlled by Eli Lilly (ELY). Lilly markets Tadalafil under the name Cialis for the indication of Erectile Dysfunction. Lilly licensed Tadalafil to United Therapeutics for the indication of PAH. Lilly controls all pricing of the drug. Tadalafil has now gone generic, and there are already generic versions of Tadalafil on the market for both Adcirca and Cialis.

Many MannKind investors were very quick to jump to the idea that United Therapeutics and MannKind would move forward for an Erectile Dysfunction indication. The first thing to grasp is that the deal between United Therapeutics and MannKind does not include the indication of Erectile Dysfunction. Thus, MannKind retains 100% of the rights for such an indication. Before we put the cart before the horse, there is a lot of ground to cover.

Decision Point for United Therapeutics

MannKind has essentially stated that it is complete with the formulation study on the "secret molecule". This means that United Therapeutics is at a decision point. It is widely expected that this decision will be a Q3 event. The decision on whether or not to move forward is purely in MannKind hands.

Even if the formulation works, it is still not a slam dunk that United Therapeutics will move forward. United CEO Martine Rothblatt has a business decision to make. In other words, is investing another $30 million into MannKind worthwhile? Remember, Tadalafil has gone generic, and the only indication that United has rights to is for treating PAH.

In order to better assess the situation, we need to go back in time. In Q3 of 2018, Tadalafil was on the verge of going generic for both PAH as well as erectile dysfunction. United's sales of Adcirca in 2017 and 2018 were as follows: